BOPs have been used for decades in oilfield operations as safety equipment for controlling a well. Blowout preventers generally are of the type designed to seal the exterior of an oilfield tubular, or are of the type designed to shear a line or tubular passing through the BOP. The present invention relates to both sealing and shearing type blowout preventers.
A significant factor relating to the utilization of blowout preventers relates to the cost of manufacturing, maintaining, and operating the equipment. Those skilled in the art of BOPs have recognized the advantages of hydraulically operated BOP rams, so that sealing assemblies or shearing assemblies can be simultaneously brought into engagement with the oilfield tubular under a substantially equal fluid pressure. Accordingly, many high-cost BOP applications supply hydraulic power to the BOP to operate simultaneously against two pistons and opposing ram assemblies to both close and open the BOP.
Relatively inexpensive blowout preventer assemblies may not easily achieve this objective because of the high cost associated with supplying continuous hydraulic power to the BOP. In lower-cost applications, BOPs may either be manually operated, or may be powered by a drive mechanism that mechanically rotates a shaft with respect to the blowout preventer body to move each ram assembly into engagement with the oilfield tubular. A manually operated blowout preventer may be closed simultaneously by two individuals, or one side of the BOP assembly may be closed, then the other side of the BOP closed. In emergency situations, the required time for safely achieving this operation is critical.
Some competitively priced blowout preventer assemblies that do not require the high cost associated with supplying the BOP with hydraulic pressure may nevertheless achieve substantially simultaneous closing of the BOP ram assemblies. The Sentinel blowout preventer manufactured and sold by Varco Shaffer, Inc. utilizes a drive motor to rotate a shaft exterior of the BOP body. Each end of the shaft is provided with a sprocket, and a pair of chains are used to simultaneously rotate the threaded shafts on opposing sides of the BOP body, thereby simultaneously closing the sealing ram assemblies on the oilfield tubular. The Sentinel BOP, however, does require the cost of a drive motor, and the exterior shaft may interfere with other equipment about the oil well recovery site. Also, the mechanical connection between a single powered drive shaft and the pair of driven shafts each housed at opposing sides of the BOP body is provided by chains, which must be properly checked and maintained.
Accordingly, there is a need to lower the cost of manufacturing and maintaining blowout preventers. There is also a need to provide a blowout preventer that will easily achieve simultaneous closing of the opposing pair of ram assemblies without incurring the cost associated with providing hydraulic fluid to power the blowout assembly rams.
The disadvantages of the prior art are overcome by the present invention, and an improved blowout preventer assembly is hereinafter disclosed. The blowout preventer of the present invention reduces the cost of manufacturing and maintaining a ram-type blowout preventer. Those skilled in the art have long sought and will appreciate the novel features of the present invention.